Debris in the coolant which collects or is trapped in fuel rod spacer grids is believed responsible for as many as 30% of known fuel rod failures. Laboratory and in-reactor experience indicate that fuel rod cladding failures can be caused by debris trapped in a grid region which reacts against the fuel rod cladding in a vibratory fashion resulting in rapid wear of the cladding. The size and shape of the debris capable of causing severe damage is quite variable. In fact, metal fragments which can only be picked up with tweezers have been known to "drill" a hole in fuel rod cladding in less than 1,000 hours of reactor operation. Since most failures occur either within or below the first spacer grid, the grids apparently provide a rather good screen for collecting debris. In order to prevent damage in the active area of the reactor, Applicant set out to design a grid structure for straining debris which: has a good probability of filtering out particles that could cause cladding damage: does not significantly increase fuel assembly uplift; does not significantly alter existing proven designs: will not jeopardize fuel rod support: will not hinder fuel assembly reconstitutability; will not significantly compromise fuel performance; has high mechanical integrity; is cost effective considering the risk/benefit; will not significantly infringe fuel rod plenum volume; and, does not require unplanned out-of-reactor flow testing.